analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

[1] Recycling of oceanic crust together with different types of marine sediments has become somewhat of a paradigm for explaining the chemical and isotopic composition of ocean island basalts. New high-precision trace element data on samples from St. Helena, Gough, and Tristan da Cunha, in addition to recent data from the literature, show that the trace element and isotope systematics in enriched mantle (EM) basalts are more complex than previously thought. EM basalts have some common characteristics (e.g., high Rb/La, Ba/La, Th/U, and Rb/Sr and low Nb/La and U/Pb) that distinguish them from HIMU basalts (high m = 238 U/ 204 Pb). The isotopically distinct EM-1 and EM-2 basalts, however, cannot be clearly distinguished on the basis of incompatible trace element ratios. Ultimately, each suite of EM basalts carries its own specific trace element signature that must reflect different source compositions. In contrast, HIMU basalts show remarkably uniform trace element ratios, with a characteristic depletion in incompatible trace elements (Rb, Ba, Th, U, and Pb) and enrichment in Nb and Ta relative to EM basalts. Compositional similarities between HIMU and EM basalts (e.g., Nb/U, La/Sm, La/Th, Sr/Nd, Ba/K, and Rb/K) suggest that their sources share a common precursor, most likely recycled oceanic lithosphere. The compositional differences between HIMU and EM basalts, on the other hand, can only be explained if the EM sources contain an additional heterogeneous component. Parent-daughter ratios in subducted marine sediments have a unimodal distribution. Recycling of sediments alone can therefore not account for the isotopic bimodality of EM basalts. The upper and lower continental crust have similarly variable trace elements ratios but are systematically distinct in their Rb/Sr, U/Pb, Th/Pb, and Th/U ratios. Thus the upper and lower continental crust evolve along two distinct isotopic evolution paths but retain their complex trace element characteristics, similar to what is observed in EM basalts. We therefore propose that recycling of oceanic lithosphere together with variable proportions of lower and upper continental crust, which are introduced into the mantle together with the oceanic lithosphere via subduction erosion and/or subduction of marine sediments, respectively, provides a plausible explanation for the trace element and isotope systematics in ocean island basalts.

Many precious, 'iron-loving' metals, such as gold, are surprisingly abundant in the accessible parts of the Earth, given the efficiency with which core formation should have removed them to the planet's deep interior. One explanation of their over-abundance is a 'late veneer'--a flux of meteorites added to the Earth after core formation as a 'terminal' bombardment that culminated in the cratering of the Moon. Some 3.8 billion-year-old rocks from Isua, Greenland, are derived from sources that retain an isotopic memory of events pre-dating this cataclysmic meteorite shower. These Isua samples thus provide a window on the composition of the Earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet. Using high-precision (less than 6 parts per million, 2 standard deviations) tungsten isotope analyses of these rocks, here we show that they have a isotopic tungsten ratio (182)W/(184)W that is significantly higher (about 13 parts per million) than modern terrestrial samples. This finding is in good agreement with the expected influence of a late veneer. We also show that alternative interpretations, such as partial remixing of a deep-mantle reservoir formed in the Hadean eon (more than four billion years ago) or core-mantle interaction, do not explain the W isotope data well. The decrease in mantle (182)W/(184)W occurs during the Archean eon (about four to three billion years ago), potentially on the same timescale as a notable decrease in (142)Nd/(144)Nd (refs 3 and 6). We speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection.

11The fate of crustal material returned to the convecting mantle by plate 12 tectonics is important for understanding the chemical and physical evolu-13 tion of the planet. Marked isotopic variability of Mo at the Earth's surface 14 o↵ers the promise of providing distinctive signatures of of such recycled ma-15 terial. However, characterisation of the behaviour of Mo during subduction 16 is needed to assess the potential of Mo isotope ratios as tracers for global 17 geochemical cycles. Here we present Mo isotope data for input and output 18 components of the archetypical Mariana arc: Mariana arc lavas, sediments 19 from ODP Sites 800, 801 and 802 near the Mariana trench and the altered 20 mafic, oceanic crust (AOC), from ODP Site 801, together with samples of 21 the deeper oceanic crust from ODP Site 1256. We also report new high pre-22 cision Pb isotope data for the Mariana arc lavas and a dataset of Pb isotope 23 ratios from sediments from ODP Sites 800, 801 and 802. The Mariana arc 24 lavas are enriched in Mo compared to elements of similar incompatibility 25 Email address: glxhf@bristol.ac.uk (Heye Freymuth)during upper mantle melting, and have distinct, isotopically heavy Mo (high 26 98 Mo/ 95 Mo) relative to the upper mantle, by up to 0.3 parts per thousand. 27 In contrast, the various subducting sediment lithologies dominantly host iso-28 topically light Mo. Coupled Pb and Mo enrichment in the Mariana arc lavas 29 suggests a common source for these elements and we further use Pb isotopes 30 to identify the origin of the isotopically heavy Mo. We infer that an aqueous 31 fluid component with elevated [Mo], [Pb], high 98 Mo/ 95 Mo and unradiogenic 32 Pb is derived from the subducting, mafic oceanic crust. Although the top few 33 hundred metres of the subducting, mafic crust have a high 98 Mo/ 95 Mo, as a 34 result of seawater alteration, tightly defined Pb isotope arrays of the Mariana 35 arc lavas extrapolate to a fluid component akin to fresh Pacific mid-ocean 36 ridge basalts. This argues against a flux dominantly derived from the highly 37 altered, uppermost mafic crust or indeed from an Indian-like mantle wedge. 38 Thus we infer that the Pb and Mo budgets of the fluid component are dom-39 inated by contributions from the deeper, less altered (cooler) portion of the 40 subducting Pacific crust. The high 98 Mo/ 95 Mo of this flux is likely caused 41 by isotopic fractionation during dehydration and fluid flow in the slab. As a 42 result, the residual mafic crust becomes isotopically lighter than the upper 43 mantle from which it was derived. Our results suggest that the continen-44 tal crust produced by arc magmatism should have an isotopically heavy Mo 45 composition compared to the mantle, whilst a contribution of deep recycled 46 oceanic crust to the sources of some ocean island basalts might be evident 47 from an isotopically light Mo signature.48 crust 50 2 portant tool to reconstruct paleo-redox conditions in the ocean (e.g. Siebert 53 et al., 2003; Arnold et al., 2004). Fractionation of Mo isotopes ...